1. Field of the Invention
The present invention relates to air bearings, novel constructions using air bearings, and novel methods using the air bearings and the constructions using them. In particular, the present invention relates to air cylinder systems, web dancer systems, and idler rolls using air bearings as an essentially frictionless implementation of movement between mechanical elements.
2. Background of the Invention
Friction between moving parts still provides one of the underlying engineering problems in the construction of mechanical elements. Friction not only induces wear on parts and materials in apparatus, but also decreases the accuracy and consistency of many mechanical devices. For example, in laser printing apparatus, even though the focus of the laser beam can be reduced in size and time controls are available for accuracy less than milliseconds, the mechanical movement of elements is hampered by friction and the attendant vibrations and irregularities introduced onto the apparatus and writing surfaces. Additionally, friction causes wear in moving parts and the variations in mechanical accuracy significantly increase with time. Wear on moving parts or on parts in contact with a moving part can necessitate regularly part replacement and down time for the equipment while the part is being replaced.
Many different contributions have been made over the years towards reducing friction between moving elements. The earliest efforts were directed towards providing smoother surfaces in contact with each other, either by improved mechanical milling, grinding or lapping, or by the application of lubricant between moving surfaces. The use of the wheel or ball bearing is another way used to reduce friction between surfaces. Mechanical bearings have ball or barrel rolling elements which have a lower friction than a bearing with elements which slide relative to each other on low friction materials such as bronze, lead, Teflon, polyethylene, or other materials. Roller bearings still require lubrication to protect the point or line contact between the spherical or cylindrical elements and their associated raceways. The lubricant is progressively squashed as a roller passes by and the shearing action present here creates friction forces and generates heat that can decompose the lubricant and/or damage the bearing surface. Some precision bearings have oversized balls installed into runways to eliminate the gaps between the ball and the raceway. This reduces the looseness of the bearing device. Each compressed ball generates friction forces due to the material damping characteristics of the ball construction material.
U.S. Pat. No. 5,810,236 (Yoshida) describes a web accumulator using a dancer roller which is mounted on a single linear ball bearing slide assembly to replace conventional support systems which use two pivot arms or two vertical guide rods. The weight of the rolls provides the web tension which is not controlled. As compared to a near zero friction air bearing pivot arm dancer roller support, this system has substantial friction in the arm support system. Nothing is taught about the use of air bearings in a roller or any other part of the system including the use of an air bearing air cylinder to control the web tension.
U.S. Pat. No. 3,995,791 (Schoppee) describes a web accumulator system which holds a sufficient amount of web material in storage that the web may continue entering the accumulator even though it is stopped momentarily to splice another roll of web. The system consists of idler rolls and driven rolls and web tension is provided by counterweights on web roll arms and also provided by friction clutch devices. Idler rolls are supported on traveling slides but no concern is expressed for the friction introduced by the slides or the rollers or the residual friction which is present in the adjustable clutch even when the activation electrical signal is turned off.
U.S. Pat. No. 4,188,257 (Kirkpatrick) describes a web splicing mechanism which uses drive motors to accelerate the web from a new roll of material to speed match the web from a near exhausted roll of material so that the two webs may be joined with adhesive tape and the old web cut away from the new. This splicing function is done on-the-fly without the use of a web accumulator system. Many web idler rolls are used in this mechanism but no concern is expressed about the amount of friction that exists in any of these idler rolls.
U.S. Pat. No. 4,028,783 (Buck) describes a system of many abrasive coated idler rolls typically used in a printing press machine which have to be changed frequently to replace the old ink contaminated abrasive surface with new clear material. Buck uses a system of telescoped abrasive sleeves which are locked on mandrels with a keyway which allows the roll replacement to be accomplished much faster than the old system. Even though the printing press has many rolls in contact with the printed web, no concern is expressed in controlling the turning friction of each of these rolls or of the total cumulative friction of all of the rolls.
U.S. Pat. No. 4,643,300 (Morrison) describes an idler roll which has antifriction bearings to reduce the rolling friction of these rolls as used in a conveyor system to allow small diameter bearings to be used without deflection of the roll shaft by making a shaft with a hollow large diameter in the middle of the roll but where the largest bending forces take place and yet using a small diameter at the ends to allow the continued use of small bearings. The dirt seals on small diameter bearings have less frictional drag than large diameter bearings so an advantage in low friction is retained with these small bearings. This beneficial feature is not discussed as the primary focus is on maintaining low cost of the idler roll. Use of extraordinary low friction air bearings in these idler rolls is not discussed.
U.S. Pat. No. 4,645,071 (Faulkner) describes a low friction idler roll where the lubricated roller bearings are replaced with solid plastic bearings which eliminates the lubrication material which is a potential contamination source to the process where the idler roll is used. Thin roll shells are used with these rolls. When foreign material enters the lubrication passageways within the roller bearing body, these bearings tend to lock up and prevent the roll from turning. Use of low friction air bearings which tend not to contaminate and also are low friction are not considered.
U.S. Pat. No. 5,709,352 (Rogers) describes a zero web tension unwinder for gossamer web material used in cigarette manufacturing which is simpler than commercial machines which are available to accomplish unwinding of fragile web material. A web is loosely stretched horizontally under a pulsed sensor with an air jet blower nozzle which applies some windage downward force on the web to stabilize it for successful position measurement of the web. A feedback control system uses the sensor output to control an unwind motor to advance the unwind roll sufficient to obtain the desired droop of the web under the sensor. Rogers is concerned about the tension effects on the fragile web but he does not address elimination of friction within the machine components such as with the use of zero friction air bearings on idler rolls, web dancer arms and within air cylinders.
U.S. Pat. No. 5,791,541 (Jitsuishi) describes a web tension control system for paper printer machines that has two dancer systems that are force activated by air cylinders. Sensors indicate the position of the dancer pivot swing arms and send signals to web brakes and to drive motors to stabilize the web tension upstream of both a web in-feed roller and the nipped print heads. A control system monitors and controls the web tension during start-up, normal operation, web break events and shut-down. No discussion is made of the friction present in the standard air cylinders, the mechanical bearings of the dancer pivot arms and the bearings in the many web rollers present in the system.
Air bearings have been used for some time in which a thin film of air passes between the moving parts, with the layer of air acting to separate the moving parts to prevent any actual physical contact between the two adjacent surfaces of the moving parts. Generally, the thickness of the air film in an air bearing is less than 0.0005 inches thick, and due to the high air pressure within the air film, the bearing is very stiff in resisting the load-carrying forces. In fact, air bearing devices are often more stiff than their mechanical bearing counterparts.
There are basically two different types of air bearings, both of which can be used in the practice of the present invention. One is a diffusion gas source device, such as a porous carbon device (with air supplied to the separation zone by diffusion through a porous material) such as those made by the New Way Machine Component Company. Another type of air bearing is a device where air is directed through gaseous conductive vents or tubes into a thin gap between machine components and the air flow rate is stabilized by passing the high pressure air through a number of small orifice jet devices which are positioned around the periphery of the air bearing. The result is a load carrying high pressure air film which exists in the gap between the bearing members.
Air cylinders typically are constructed with O-ring seals on a rod piston which slides on or in a cylindrical housing. One end of the cylinder may be pivotally fixed to a surface, and a plunger compresses air within a chamber as it moves towards that surface within the cylinder housing. The O-ring seal merely assists in maintaining the pressure within a compression zone at one end of the cylinder.
Air bearing web dancer systems are used in web carrying or transporting systems, particularly where elimination of friction in web idler rolls is very important. This is a specialized use of air bearing cylinders.
Generally, very low friction is desired for thin, weak webs such as 0.005 inches or less or 0.001 inch or less in thickness. The composition of the web may be any substance that may be subject to damage when moved under stress, such as polymers, fibrous materials (e.g., artificial papers), ceramics papers, and particularly porous polyethylene or polypropylene film or web materials. It is also important to have very low friction for other types of webs to achieve effective coating or slitting or other processing and to assure accurate movement of transported materials.
Web dancer systems are used to control the web tension in a span of web that is being processed in web manufacturing machines or web processing machines. Another use of low friction idlers is in web dancer systems. Here a web is typically wrapped 180 degrees around a moving idler roll which is mounted on a pivot arm. This pivot arm is then activated by an air cylinder which results in the cylinder force being imparted to the web which is routed by the use of two stationary idler rolls. Rotational friction in any of the three rolls imposes added web tension to the web independent of the web tension created by the pressure controlled air cylinder. Many efforts have been made to create zero friction web dancer systems, including the use of techniques where a web is contained in a box and vacuum draws the web deep into the box and the web is routed into and out of the box by use of air turn devices. The air turn half cylinder shapes are pressurized internally with air which escapes radially through orifice holes to create an air film between the web and the air turn. As the web does not contact any of the structural components of the vacuum dancer device, no friction is imparted to affect the web tension. A disadvantage is that these devices cannot produce very high web tensions and are inherently unstable.
Idler rolls are used to provide low friction points of support of materials during transportation, particularly for transportation of elongate materials, such as fiber, yarn, sheet or film materials. A primary use of idler rolls is for web systems where continuous rolls of paper or plastic are processed through extruding or coating machines, longitudinal or cross-web stretching equipment, web coaters, inspection stations, web slitters, winders, converting equipment, and the like
In addition, there is need for extra low friction rollers for use in conveyor idler roller systems. Further, many other processes require low friction idler rolls such as for routing of thin plastic filaments from extruder/spinneret systems, the coating of thin wires, the transfer of parts in assembly machines, printing presses, strand winding equipment, tape applications machines, web steering equipment, paper making equipment and other uses.
Idler rolls are used in many types of web processing equipment to route and steer continuous sheets of web through a machine. The largest forces on a roll are those perpendicular to the axis of the roll as imposed by the combination of forces from web tension as the web enters the roll and also as it exits the roll. Normally, there is a lesser force along the axis of the roll which originates from web forces induced when a web is not precisely perpendicular to the axis of a roller as the web enters or exits a roller.
When precision web tension is desired in one of these rollers (the dimensions of which are often referred to as the web span), web tension is typically established by a motor which supplies torque to a roll about which the web is wrapped with sufficient friction that the web does not slip on the surface of the driven roll. The torque applied to the roll by the motor is then transmitted to the web to produce the desired web span tension. Each web idler roll that is installed within a controlled tension web span will change this web span tension downstream of the idler due to the added rotational friction of the idler roll. This change of web tension can be critical to the successful processing of the web in that span zone. For instance, the thickness of a liquid coating applied to coating stations is changed by the tension of the web within the span which bridges across the coating station. Web tension control (for example when coating multiple layers of coating fluids on photographic imaging web material such as polyester or cellulose triacetate) is critical to successful coating. Great efforts have been made in the past using techniques such as installing roller bearings within concentric roller bearings. Also, when a magnetic tape web is slit to a very precise width, the web tension of the web that bridges the slitter head affects the final width of the magnetic tape strand. This affect occurs because the web is reduced in cross width the more it is stretched longitudinally due to high web span tension. If the tape is precisely slit to a given width while under great web tension, the tape will then relax to become oversized in width after it passes the slitter station and has its web tension relaxed prior to winding on a roll.
For use in web systems, elimination of friction in web idler rolls is very important. Generally, very low friction is desired for thin weak webs such as 0.001 inch or less thick porous polyethylene or polypropylene. It is also important to have very low friction for other types of webs to achieve effective coating or slitting or other processing.
Another use of low friction idlers is in web dancer systems. In that type of system, a web is typically wrapped 180 degrees around a moving idler roll that is in turn mounted on a pivot arm. This pivot arm is then activated by an air cylinder which results in the cylinder force being imparted to the web which is routed by the use of two stationary idler rolls. Rotational friction in any of the three rolls imposes added web tension to the web independent of the web tension created by the pressure controlled air cylinder. Many efforts have been made to create zero friction web dancer systems, including the use of techniques where a web is contained in a box and vacuum draws the web deep into the box and the web is routed into and out of the box by use of air turn devices. The air turn half cylinder shapes are pressurized internally with air which escapes radially through orifice holes to create an air film between the web and the air turn. As the web does not contact any of the components of the vacuum dancer device, no friction is imparted which affects the web tension. A disadvantage is that these devices cannot produce very high web tensions and are inherently unstable.
Idler rolls typically are designed with an external shell and a mechanical bearing at each end. These bearings are usually mechanical roller bearings and often include sleeve type sliding contact bearings. Other more sophisticated rolls employ magnetic suspension devices to eliminate contact between two given parts. Most roller bearings have mechanical seals which retain lubrication within the bearing housing and prevent foreign material from entering. Some low friction, loose fitting roller bearings are manufactured that eliminate seals which rub on the surface of the bearing and which are given low viscosity lubricants. Contamination of the roller bearing is a problem as particles act as wedge blocks between the rollers and the bearing braces.
Air bearings such as the porous carbon shell type units manufactured by New Way Machine Components, Inc. can be used to handle the radial forces on an idler roll but they do not have a way of addressing the axial thrust forces on the roll. It is therefore desirable to provide an idler roll described here handles both the radial and thrust loads on a roll with air bearing support on both the radial shaft surface and the axial end surface.
A near-zero friction linear motion air cylinder can be combined with a near-zero friction idler roll to form a near-zero friction web dancer system. Both the air cylinder and the idler roll use air bearings that provide near-zero friction movement of one machine element relative to another either with linear motion or rotary motion. This web dancer system can provide controlled web tension in a span of web without imparting extra web tension to the web due to friction of the dancer components. The same cylindrical shell type air bearing having porous (e.g., porous carbon) elements surrounding (on at least opposed or three point support) a shaft can provide either linear or rotary motion of the system components.
In addition, these same air bearing type devices can be used for the Dancer pivot arms or a dancer slide to create near-zero friction in these dancer components that may be used in conjunction with the air cylinders and the idler rolls.
There essentially is no friction in these machine motions because the component parts are separated by a very thin film of air that is introduced into the very small gap which exits between the parts by use of an air bearing device. Normally, this gap is filled with a lubricant having a viscosity much greater than air. When one component part is moved relative to another, the two parts slide relative to each other and develop a shearing force on this thin layer of high viscosity lubricant. This shearing force is the source of the friction between the two moving parts which prevents one part from moving freely relative to the other part. This friction force not only resists motion of the moving piece, but it also creates heat which will raise the temperature of the local area. The lubrication in most bearings is sealed within the bearing and is not recirculated to a cooling device, so the temperature builds to such a high level that heat is then successively transferred to other adjacent machine members by conduction, convection or radiation. An air bearing naturally provides a cool operating bearing device for a number of reasons. First, a high pressure compressed air source is used and this air expands as it is passed through the bearing. The temperature of this room temperature air is reduced proportionally to the change in pressure as a function of Boyle""s Law which results in cooling air being continuously supplied to the bearing. Next, the viscosity of air is typically only about one thousandth that of a lubricating grease, so the amount of heat generated in the bearing joint is reduced by this large factor. Third, a semi-permanent lubricated bearing typically has a thin flexible plastic or metal shield which is used as a barrier to prevent debris from entering the internal structure of the bearing. To effect a complete seal, this thin shield is normally attached to one part of the bearing and rubs against the other moving portion of the bearing with some residual friction force due to this rubbing action.
FIG. 1 has four views of a air bearing air cylinder with gimbal type support mounts. FIGS. 1a) and 1d) are cross sectional views and FIGS. 1b) and 1c) are perspective views.
FIG. 2 is two side views of a web dancer system. FIG. 2a) shows a pivot arm web dancer and FIG. 2b) shows a linear slide web dancer.
FIG. 3 is a cross sectional view of a fluid bearing roller.
FIG. 4 is a cross sectional view of an air bearing idler roll and roller.
FIG. 5 is a cross sectional view of an air bearing idler roll.
FIG. 6 is a cross sectional view of a cone shaped air bearing.
FIG. 7 is a cross sectional view of a ball with a cone seat.
FIG. 8 is a cross sectional view of a dual shaft air bearing.
FIG. 9 is a cross sectional view of a relieved sphere cup seal.
FIG. 10 is a cross sectional view of a floating ball cup seal.
FIG. 11 is a cross sectional view of a non spring loaded radial floating cup.
FIG. 12 is a cross sectional view of an axial air bearing piston.
FIG. 13 is a cross sectional view of shaft air bearing pistons.
FIG. 14 is a cross sectional view of an air bearing with shaft chamber.
FIG. 15 is a cross sectional view of a shaft with one axially rigid end.
FIG. 16 is a cross sectional view of a Belview washer spring.
FIG. 17 is a cross sectional view of a flat air bearing shaft end.
FIG. 18 is a cross sectional view of a pivot ball flat disk end.
FIG. 19 is a cross sectional view of a ball post axial restraint.
FIG. 20 is a cross sectional view of a single axial thrust bearing.
FIG. 21 is a cross sectional view of dual ball link arms.
FIG. 22 is a cross sectional view of a spring loaded linkage arm without roll shell.
FIG. 23 is a cross sectional view of a spring loaded linkage arm with roll shell.
FIG. 24 is a cross sectional view of an air bearing roll with passive air.
FIG. 25 is a cross sectional view of an air bearing roll with passive adjustable shaft gap.
FIG. 26 is a cross sectional view of a roller axial adjustable bearing.
FIG. 27 is a cross sectional view of a roll with annular air bearing.
FIG. 28 is a cross sectional view of an air bearing roll assembly.
FIG. 29 is a cross sectional view of grinding of roll thrust bearing.
FIG. 30 is a cross sectional view of an exposed shaft air bearing roller.